A hybrid vehicle may be provided with a driveline disconnect clutch. The driveline disconnect clutch may be closed to couple an engine with an electric machine. The driveline disconnect clutch may be opened to decouple the engine from the electric machine. The engine may provide torque to the driveline when the driveline disconnect clutch is closed. The engine is stopped when the driveline disconnect clutch is open to conserve fuel. However, decoupling the engine from the driveline in response to a reduction in torque demand may change the driveline inertia and may result in a driveline torque disturbance. Further, restarting a stopped engine takes time, and a delay in engine restarting may result in a reduction in driveline torque response.
The inventors herein have recognized the above-mentioned disadvantages and have developed a driveline operating method, comprising: providing torque from an engine to a driveline coupled to wheels; operating the engine at an idle speed and decoupling the engine from the driveline in response to a reduced driver demand torque; and providing a constant vehicle deceleration rate during the reduced driver demand torque.
By decoupling an engine from a driveline and allowing the engine to idle, it may be possible to conserve fuel and respond quickly to an increase in desired torque. Additionally, providing a constant vehicle deceleration rate during the reduced driver demand torque may reduce the likelihood of a driver recognizing that the engine is decoupled from the driveline. For example, it may be possible to reject driveline torque disturbances and provide a constant rate of vehicle deceleration when a driveline integrated starter/generator is operated in a speed control mode.
The present description may provide several advantages. For example, the approach may reduce driveline torque disturbances of a hybrid driveline. Further, the approach may improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.